Begin your letter by mentioning the post you are applying for and the source from where you came to know about the vacancy.

The mid-section of your letter should be one or two short paragraphs mentioning relevant points. You should not summarize your resume. You may incorporate a column to bullet point format here.

Your last pargraph (closing line) should initiate action or sitimulate the reader to call you for an interview.

[In short, the body contains the arguments that support your eligibilty and better suitability for the positon applied for. One should carefully choose what to include in the arguments. Because the speace is very limited. The arguments should be powerful, relevant and creative. One should take care that the reader (the hiring authority / official) must not be boged down with details about your past or other irrelevnt things.]